The emitter follower stage (also known as the common collector stage) is widely used in analog circuit designs. Its uses include buffering, level-shifting, and as an output stage. Some of the characteristics used to measure a good emitter follower stage are high input impedance, low input current, low output impedance, low gain compression, low distortion, and a gain that is near unity. Since these characteristics are desirable, there is a continuing need in the art to improve them.
One improvement over the basic emitter follower that improves at least some of these characteristics over the basic emitter follower is described in U.S. Pat. No. 4,891,607, titled LOW DISTORTION DRIVE AMPLIFIER which is hereby incorporated herein by reference. However, this design involves a differential input, and works best with a constant load impedance and a conventional amount of input current.
Accordingly, there is a need in the art for an emitter follower stage with a single-ended input that works well with different load impedance's and also has high input impedance, low input current, low output impedance, low gain compression, low distortion, and gain that is near unity.